The invention relates to a liquid filter assembly for removing impurities contained in a liquid, and more particularly, to such an assembly including a filter in the form of a roll through which a liquid is passed for filtering action.
A liquid filter assembly including a filter in the form of a roll which separates and recovers impurities contained in a liquid is known in the art. The filter comprises a roll of paper sheet when the liquid is to be filtered is oily, and comprises a roll of synthetic resin sheet such as polypropylene when the to be filtered is aqueous. The roll is coaxially received in a cylindrical shell, and contaminated liquid to be filtered is pumped to the top of the shell for filtering purpose. In the use of such assembly, as contaminated liquid is passed through the top of the roll filter, the adsorption of sludges begins from the top of the filter, causing a plugging which produces a resistance to the passage of the contaminated liquid. If the supply of contaminated liquid is continued when the passage thereof through the filter encounters an increased resistance, the supply pressure increases, which causes cracks to be produced in a portion of the roll filter. The cracks produced in the filter tend to be widened under the pressure of the contaminated liquid, allowing the contaminated liquid to be externally discharged through these cracks and a drain port without being filtered, thus degrading the filtering performance. While the occurrence of cracks may be prevented by reducing the supply pressure of the contaminated liquid, this reduces the filtering efficiency.